In the Garden:
The aphids on this Mexican milkweed are food for a ladybug larva, a syrphid fly larva, and numerous parasitoid wasps (inside brown aphids).
Invite Beneficial Insects to Your Garden
If you build it they will come. Our gardens are home to a wide variety of insects including many pests and beneficial insects. When we make our gardens attractive to beneficial insects, they do their job of keeping nature in balance. In my last column I talked about the most common beneficials that you're apt to see, and now I'll share some tips for making your garden a welcoming home for these insects.
Avoid Broad-Spectrum Sprays
Some pesticides are broad spectrum in that they destroy a wide variety of insect species. Others are more targeted to only one type of insect or one stage of an insect's life. Broad spectrum sprays tend to upset the balance of nature more, often resulting in an outbreak of another type of pest by killing insects that were previously keeping them in control.
Narrow spectrum sprays are a preferred choice because they work more like an arrow than a grenade, targeting a particular pest without so many unintended consequences. Bacillus thuringiensis or Bt is an example of a narrow spectrum spray. It works on caterpillars but doesn't harm ladybugs, lacewings, or other beneficial insects. It will, however, kill butterfly larvae so don't apply it to plants that are larval food sources for butterflies.
A source of water such as a birdbath with some stones in the water to make it more accessible for small insects will make your garden a more attractive place for beneficials. Drip irrigation, occasional sprinkling, or a water feature can also provide a source of water to attract some types of beneficial creatures.
Pollen and Nectar
Some types of beneficial insect adults do not feed on pests but rather require pollen and nectar for energy. Examples include many of the small parasitoid wasps, lacewings, and syrphid or hover flies. We can plant flowers with small blooms that attract these types of good guys to the garden.
Flowers with small daisy-like blooms, such as chamomile, feverfew, fall asters, coneflowers, and black-eyed Susans work well. So do plants with umbrella-like flowerheads like anise, yarrow, fennel, coriander (cilantro), and dill. Many herbs also have attractive flowers, including thyme, chives, oregano, basil, and rue.
Yes, you need to have pests in order to have beneficial insects. These helpful gardening allies are not philanthropic! They come to our gardens because they contain something to aphids, caterpillars, insect eggs, and other food sources. Having a few pests around, in moderation of course, means that we will also have beneficials around to help prevent major pest outbreaks.
If we learn to tolerate a few pests as a good thing, we'll find our gardens are a more welcoming home for beneficial insects. I like to plant Mexican or tropical milkweed. This plant attracts a yellow aphid that doesn't seem to harm the plant but does bring in a number of different beneficial insects, including ladybugs, lacewings, parasitoid wasps, and syrphid flies. These beneficials lay eggs on the plant that will hatch out into numerous additional beneficials that will soon be flying about my garden looking for other pests and keeping them from getting out of control.
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